Disclosed herein are phase change ink formulations. More specifically, in one embodiment, disclosed herein are phase change ink formulations containing an ink base, a dispersant and a pigment colorant. In another embodiment, disclosed herein are phase change ink formulations containing an ink base, a dispersant, a pigment colorant, and a synergist.
In general, phase change inks (sometimes referred to as “hot melt inks”) can be in the solid phase at ambient temperature, but exist in the liquid phase at the elevated operating temperature of an ink jet printing device. At the jet operating temperature, droplets of liquid ink can be ejected from the printing device and, when the ink droplets contact the surface of the recording substrate, either directly or via an intermediate heated transfer belt or drum, they quickly solidify to form a predetermined pattern of solidified ink drops. Phase change inks have also been used in other printing technologies, such as gravure printing, as dcan disclosed in, for example, U.S. Pat. No. 5,496,879 and German Patent Publications DE 4205636AL and DE 4205713AL, the disclosures of each of which are totally incorporated herein by reference.
Phase change inks for color printing typically comprise a phase change ink carrier composition which can be combined with a phase change ink compatible colorant. In a specific embodiment, a series of colored phase change inks can be formed by combining ink carrier compositions with compatible subtractive primary colorants. The subtractive primary colored phase change inks can comprise four component dyes, namely, cyan, magenta, yellow and black, although the inks are not limited to these four colors. These subtractive primary colored inks can be formed by using a single dye or a mixture of dyes. For example, magenta can be obtained by using a mixture of Solvent Red Dyes or a composite black can be obtained by mixing several dyes. U.S. Pat. No. 4,889,560, U.S. Pat. No. 4,889,761 and U.S. Pat. No. 5,372,852, the disclosures of each of which are totally incorporated herein by reference, teach that the subtractive primary colorants employed can comprise dyes from the classes of Color Index (C.I.) Solvent Dyes, Disperse Dyes, modified Acid and Direct Dyes, and Basic Dyes. The colorants can also include pigments, as disclosed in, for example, U.S. Pat. No. 5,221,335, the disclosure of which is totally incorporated herein by reference. U.S. Pat. No. 5,621,022, the disclosure of which is totally incorporated herein by reference, discloses the use of a specific class of polymeric dyes in phase change ink formulations.
Phase change inks can have also been used for applications such as postal marking, industrial marking, and labeling. Phase change inks can be desirable for ink jet printers because they remain in a solid phase at room temperature during shipping, long term storage, and the like. In addition, the problems associated with nozzle clogging as a result of ink evaporation with liquid ink jet inks can be largely eliminated, thereby improving the reliability of the ink jet printing. Further, in phase change ink jet printers wherein the ink droplets can be applied directly onto the final recording substrate (for example, paper, transparency material, and the like), the droplets solidify immediately upon contact with the substrate, so that migration of ink along the printing medium can be prevented and dot quality can be improved.
Compositions suitable for use as phase change ink carrier compositions are known. Some representative examples of references disclosing such materials include U.S. Pat. No. 6,309,453, U.S. Pat. No. 6,858,070, U.S. Pat. No. 7,311,768, U.S. Pat. No. 7,442,242, U.S. Pat. No. 7,655,084, and U.S. Pat. No. 7,973,186, the disclosures of each of which are totally incorporated herein by reference.
While known compositions and processes can be suitable for their intended purposes, a need remains for improved phase change inks. In addition, a need remains for phase change inks having carbon black pigment wherein the pigment particles can be stable and uniformly dispersed within the ink formulation, and can have increased stability and light fastness at elevated temperatures, thereby enabling improved fade resistance upon exposure to heat and/or light. In addition, there is a need for phase change inks containing carbon black pigments that exhibit reduced diffusion of the colorant from the ink to paper, thereby enabling reduced show through and improved image quality. Additionally, there is a need for phase change inks containing carbon black pigments wherein the pigments exhibit reduced agglomeration and settling in the ink when the ink is exposed to prolonged and/or excessive heating conditions. A need also remains for phase change inks containing carbon black pigments that exhibit reduced clogging of jets in the print head and reduced print head failure that might be caused by agglomeration of the pigment colorant in the ink.